1. Field of the Invention
This invention relates to disk head assemblies for supporting read/write heads adjacent rotating disks in disk drives and more particularly, to a base plate for attaching a load beam assembly to a head actuator arm.
2. Description of the Prior Art
In hard disk drives data are stored on magnetizable surfaces of a plurality of rotatable disks that are mounted in a coaxial stack on a housing of the drive. Transducer heads that write to and read data from the disk surfaces are supported by an actuator that is mounted on the housing and can be actuated to position the transducer heads in alignment with concentric data tracks defined on the disks. Each transducer head is attached to one end of a transducer support arm that is connected to an actuator arm that extends from the actuator body. The support arms include a flexible load beam constructed of light sheet steel that will flex sufficiently to permit air turbulence caused by the rotating disks to lift the heads slightly off of the disks so that the heads fly on an air bearing across the disk surfaces.
In the past, head-carrying load beams have been attached to the actuator arms using base plates that form a part of the transducer support arms. Each base plate includes a flat flange portion and a cylindrical hub portion or boss. The base plate hub is passed through a load beam boss hole and the flange is spot welded to the load beam. The combined base plate and load beam is called a transducer support arm, and each support arm has the hub of the base plate extending through and beyond the load beam boss hole.
The hubs of two support arms are inserted into each of a series of actuator arm boss holes formed through a plurality of actuator arms extending from the actuator body, one hub entering an actuator arm boss hole from each end of the hole. A swage ball is passed through the cylindrical hubs to force the peripheries of the hubs to expand (swage) into tight engagement with the inner peripheries of the actuator arm boss holes. Thus, each actuator arm carries two support arms on opposite sides thereof to support two transducer heads in opposing directions in close proximity with the surfaces of two disks in the assembled hard disk drive.
Problems with this method of mounting transducer heads have arisen as the need for increased data storage capacity in hard disk drives has grown and the size of the disk drive has decreased to fit in small lap top computers. The problem of forming a strong connection between the actuator arms and the transducer support arms has been made more difficult as the thickness of the components has become smaller.
Because of the joining of two transducer support arms to each actuator arm by passing a ball through two hubs in the same hole in the actuator arm, an asymmetry exists in the forces that are exerted on the hubs to make the joints. Because the transducers face in opposite directions, the hubs on their respective load beams also extend in opposite directions with respect to the direction of passage of the ball through the inner diameters of the hubs. For one transducer support arm, the ball is passed in a direction that tends to place the hub in compressive stress while, for the other transducer support arm, the direction of passage of the ball is such as to tend to place the hub in tensile stress. Placing a hub in tensile stress during the swaging operation that joins the transducer support arms to an actuator arm will often result in a weak joint between the hub and the actuator boss hole. In order to prevent rupturing of the hub, resulting in a weak joint, the expansion of the hub during swaging must be limited and such limitation will limit the contact forces between the hub and the actuator arm boss hole periphery, forming a weak joint.
An important measure is the gram load parameter at the transducer slider of a load beam before and after swaging. In the prior art, transducer sliders on load beams swaged in the tension direction do not exhibit the same performance as transducer sliders on load beams swaged in the compression direction. What is desired is a head stack for which the same amount of force is transmitted to the slider from the load beam, that is the same gram load. For example, when a swage ball is run through the head stack, the gram force may gain +0.4 grams in the tension direction and lose -0.1 grams in the compression direction. If the target gram load force for each slider is 3.5 grams, in the prior art it has been necessary to start with 3.6 grams for compression direction load beams and 3.1 grams for tension direction load beams in order to achieve the same target gram load force for all sliders in the head stack. This complicates the manufacturing process. What is needed is a base plate that does not lose or gain gram load as a result of the swaging process, and is the same for both the tension swage direction and the compression swage direction.
It is therefore an object of this invention is to provide a base plate that exhibits similar swage performance in the tension and compression swage directions.